局部变量空指针异常

Question

当我单击登录类上的注册按钮时，我收到一个空指针异常，它给出了该错误。我试图修改局部和全局变量，但似乎没有什么可以解决错误，我可能在 onClickListener 上混淆了，因为当我删除该代码时它似乎可以工作。

注册.class。

public class Signup extends Activity {
    /*List Variables */ 
    private ScrollView scrollView1;
    private EditText editTextUN;
    private EditText editTextPW1;
    private EditText editTextPW2;
    private EditText editTextEMAIL;
    private Button buttonSignup;
    private Button buttonCancelSignup;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        /*set ContentView */
        setContentView(R.layout.signup);
        /*Populate fields */
        populate();

    }
    private void populate() {
        // TODO Auto-generated method stub
        /*initialize the ScrollView */
        ScrollView scrollView1 = (ScrollView) findViewById(R.id.scrollView1);
        /*initialize the EditText for the FIRST username field */
        final EditText editTextUN = (EditText) findViewById(R.id.editTextUN);
        /*initialize the FIRST password field */
        final EditText editTextPW1 = (EditText) findViewById(R.id.editTextPW1);
        /*initialize the SECOND password field */
        final EditText editTextPW2 = (EditText) findViewById(R.id.editTextPW2);
        /*initialize the signup Button */
        Button buttonSignup = (Button) findViewById(R.id.btsignup);
        /*initialize the cancel Button */
        Button buttonCancelSignup = (Button) findViewById(R.id.buttonCancelSignup);
        /*initialize the email EditText */
        final EditText editTextEMAIL = (EditText) findViewById(R.id.editTextEMAIL);
        /*setup OnClickListener */
        buttonSignup.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                // TODO Auto-generated method stub
                /*check to see if it's the signup button */
                if(v.getId()== R.id.buttonSignup) {
                    /*get everything to a string */
                    String user = editTextUN.getText().toString();
                    String pass1 = editTextPW1.getText().toString();
                    String pass2 = editTextPW2.getText().toString();
                    String email = editTextEMAIL.getText().toString();

                    /*check to see if there's Text in all the Edit Text's */
                    if(user !=null && user.length()>5 && pass1.length()>5 && pass1 !=null && pass2.length()>5 && pass2 !=null && email.length()>5 && email !=null) {
                        /*send to comHelper */
                        ComHelper.sendSignUp(user, pass1, pass2, email);
                        while(ComHelper.sendSignUp(null, null, null, null)) {
                        }

                    }

                } else {
                    finish();
                }

            }
        });
    }


}

日志猫：

06-06 17:15:30.045: E/AndroidRuntime(1197): FATAL EXCEPTION: main
06-06 17:15:30.045: E/AndroidRuntime(1197): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gta5news.qwuik/com.gta5news.qwuik.Signup}: java.lang.NullPointerException
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.os.Looper.loop(Looper.java:137)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.main(ActivityThread.java:4424)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at java.lang.reflect.Method.invokeNative(Native Method)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at java.lang.reflect.Method.invoke(Method.java:511)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at dalvik.system.NativeStart.main(Native Method)
06-06 17:15:30.045: E/AndroidRuntime(1197): Caused by: java.lang.NullPointerException
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.gta5news.qwuik.Signup.populate(Signup.java:70)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.gta5news.qwuik.Signup.onCreate(Signup.java:40)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.Activity.performCreate(Activity.java:4465)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

编辑：这是在x86模拟器上。

Answer 1

上述所有陈述都是正确的，但我认为NullPointerException是由于：

因为右in Button buttonSignup = (Button) findViewById(R.id.btsignup); ID是R.id.buttonSignup

所以看起来按钮注册在那里为空

正如您在

......

......

/*

检查是否是注册按钮 */

            if(v.getId()== `R.id.buttonSignup`) {

......

......

Answer 2

我已经

更新了您的代码并添加了注释，现在它对我来说工作正常

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ScrollView;
import android.widget.Toast;
public class Signup extends Activity {
    /*List Variables */ 
    private ScrollView scrollView1;
    private EditText editTextUN;
    private EditText editTextPW1;
    private EditText editTextPW2;
    private EditText editTextEMAIL;
    private Button buttonSignup;
    private Button buttonCancelSignup;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.signup);
        /*Populate fields */
        populate();
      }
    private void populate() {
        
        /*initialize the ScrollView */
        ScrollView scrollView1 = (ScrollView) findViewById(R.id.scrollView1);
        /*initialize the EditText for the FIRST username field */
        final EditText editTextUN = (EditText) findViewById(R.id.editTextUN);
        /*initialize the FIRST password field */
        final EditText editTextPW1 = (EditText) findViewById(R.id.editTextPW1);
        /*initialize the SECOND password field */
        final EditText editTextPW2 = (EditText) findViewById(R.id.editTextPW2);
        /*initialize the signup Button */
        
        /* here.........i have added final .........*/
       final  Button buttonSignup = (Button) findViewById(R.id.btsignup);
        /*initialize the cancel Button */
        Button buttonCancelSignup = (Button) findViewById(R.id.buttonCancelSignup);
        /*initialize the email EditText */
        final EditText editTextEMAIL = (EditText) findViewById(R.id.editTextEMAIL);
        
        /*setup OnClickListener */
        buttonSignup.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                // TODO Auto-generated method stub
                /*check to see if it's the signup button */
                //if(v.getId()== R.id.btsignup) {
                
                /* here.........i have added if condition .........*/
                    if(v==buttonSignup){
                        Toast.makeText(getApplicationContext(), "button has been pressed", Toast.LENGTH_SHORT).show();
                        
                    /*get everything to a string */
                    String user = editTextUN.getText().toString();
                    String pass1 = editTextPW1.getText().toString();
                    String pass2 = editTextPW2.getText().toString();
                    String email = editTextEMAIL.getText().toString();

                    /*check to see if there's Text in all the Edit Text's */
                    if(user !=null && user.length()>5 && pass1.length()>5 && pass1 !=null && pass2.length()>5 && pass2 !=null && email.length()>5 && email !=null) {
                                                
                   }
                } 
                else 
                {
                    finish();
                }
            }
        });
    }
}